The use of semiconductor diodes per se to provide the capacitive shunt elements of a rf detector-filter circuit is known. See for example U.S. Pat. No. 3,290,516 (Nishizawa) which describes the equivalent filter circuit resulting from the interaction of distributed inductance and diode capacitance with a continuous, helical wire is wound inside a cylindrical sheath and semiconductor diodes are connected directly between the wire and sheath. This particular arrangement provides a bandwidth having an upper limit at approximately 400 Mhz.
Ideally, a video detector will exhibit a good VSWR (less than 2:1) over its bandwidth and its transfer characteristic will follow a square law relationship (i.e., V.sub.out =.gamma.P.sub.IN) over all ranges of input power. Known video detectors exhibit a VSWR of about 2.5:1 over a RF bandwidth of 2 to 18 GHz and their transfer characteristic follows the square law relationship only below -15 db input power.
The present invention realizes a wide band, travelling wave video detector by utilizing the parasitic junction capacitance of semiconductor diodes in an artificial transmission line. The detector exhibits a good VSWR (less than 2:1) over its RF bandwidth (100 GHz) and its transfer characteristic closely follows the square law relationship for power input levels above -15 db while retaining an acceptable video bandwidth (100 MHz).